Birds in female-dominated populations are more likely to dump or 'divorce' their mates while promiscuity increases in predominantly male environments, scientists claim

THE BEHAVIOUR OF BIRDS

Rates of infidelity in birds are affected by the adult sex ratio of the population they live in

Birds in female-dominated populations are more likely to dump or ‘divorce’ their mates, according to the study.

Promiscuity increases in predominantly male environments.

Both sexes are more polygamous when the ratio was skewed towards the opposite sex.

'The rare sex has more opportunity to 'play the field' and cheat,' the researchers said.

A joint study by the University of Sheffield and the University of Bath claims to have proved, for the first time, that rates of infidelity in birds are affected by the adult sex ratio of the population they live in – a theory previously discounted by biologists.

RELATED ARTICLES

Share this article

The study examined mating behaviour and bonding of 197 different species of bird and found the divorce rate is higher in species with a female-biased sex ratio.

However, when the number of male birds outweighs females, the frequency of cheating increases in typically monogamous species.

The study, which was published in the journal Current Biology, found that both sexes are likely to have multiple partners when the ratio was skewed towards the opposite sex.

‘If there is more of one sex than another, members of the rarer sex have a higher chance of getting a new partner for breeding than members of the common sex, said Professor András Liker, Marie Curie Research Fellow at the University of Sheffield during the study.

‘Basically, the rarer sex has more opportunity to 'play the field' and either cheat on the partner or leave in favour of a new mate.

‘Many animals form pairs to mate and then look after offspring. However, in animals as well as in humans, couples may not be permanent – divorce and infidelity are remarkably common.’

Professor Tamás Székely, of the
Biodiversity Lab at the University of Bath, said the researchers were
interested in watching both sexes ‘play the game’.

‘If there are lots of unpaired members of the opposite sex, there is more opportunity for the rarer sex to attract several partners.

‘We found that a female bias in sex ratio destabilises the pair bond system, although it is unclear as to whether this is due to lots of unpaired females luring males away from their mate or if the male, given a greater choice of partners, decides to switch partners more frequently.

Researchers have proved for the first time that rates of infidelity in birds are affected by the adult sex ratio of the population they live in - a theory previously discounted by biologists. An image of geese in flight is pictured

‘We also found that extra-pair mating was more common when there were more males than females - this could be due to females “shopping around” when they have more males to choose from, or it could be that there is more rape by males unable to secure a permanent mate.’

Professor Robert Freckleton, of the University of Sheffield’s Department of Animal and Plant Sciences, believes the role that sex ratio plays in human mating behaviour should be studied further in light of the research.

‘Surprisingly, some of our results in birds have striking parallels in human societies – for example, the frequency of divorce is related to sex ratio in some human societies in the same way.

‘These results suggest that adult sex ratio may have an important role in shaping mating behaviour in a wide range of organisms and deserve further investigations both in humans and non-human animals,’ he added.